1. Field of the Invention
The invention relates to a heat-sensitive recording material, a heat-sensitive recording method and a method for manufacturing a heat-sensitive recording material. More specifically, the invention relates to heat-sensitive recording materials with little head staining and low torque transport that are suitable for medical heat-sensitive recording materials, multicolored heat-sensitive recording materials, and the like, a method for manufacturing such heat-sensitive recording materials, and a heat-sensitive recording method using the heat-sensitive recording materials.
2. Description of the Related Art
In recent years, the heat-sensitive recording method has been developing in various fields since the method has, for example, the following advantages: (1) no development is necessary, (2) if the support for a heat-sensitive recording material is paper, the material is similar to standard paper, (3) operation is easy, (4) color density of the resultant image is high, (5) a recording device is simple, highly reliable and inexpensive, (6) no noise occurs at the time of recording, and (7) no maintenance is needed. The use of the heat-sensitive recording method has been expanding over the field of facsimiles and printers, the field of labels such as POS, and other fields.
With this background, in recent years, transparent heat-sensitive recording materials that can be applied to multicoloring, or can project an image or the like by an overhead projector, and can directly record an image on a light table, and heat-sensitive recording materials that can perform multicolored recording, have been developed.
In such transparent heat-sensitive recording materials, an image is formed, generally, through press bonding a heat-sensitive recording material to a thermal head by the use of a platen roll and applying heat in a pulsing state with the thermal head while transporting the heat-sensitive recording material by the platen roll or a driving gear installed separately. At this time, if the friction coefficient between the thermal head and the recording material is large and the fluctuation range is large, the transfer speed becomes not uniform and a density difference is generated in the main scanning direction of the head. Although the density difference is rarely a problem in the binary recording for facsimiles and POS, the density difference may be noticeable in printer use in which a gradation image is output and may deteriorate the image quality. For that reason, decreasing the friction coefficient between the thermal head and a material has previously been proposed (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 2002-144735 and 2004-338360); however, because the friction coefficient between the thermal head and the material depends on printing energy, density difference may yet occur in a medical image in which a wider dynamic range is needed, and improvement of this aspect is desired.
Moreover, in a heat-sensitive recording material in which multicolor recording is needed, printing of each color has been carried out separately over a number of times. While the addition of various kinds of lubricants in the protective layer has been carried out for the purpose of improving the prevention of head staining and the like (for example, see JP-A Nos. 6-340179 and 2002-362029), an unresolved problem is that dislocation in the positions of the sheet between early printing and the later printing (so-called disagreement in registration) occurs when the fluctuation range of the friction coefficient between the thermal head and the recording material is large, and improvement of this problem is desired.